The increased demand for even more compact and lightweight computer systems has fostered a need for smaller disk drives and accompanying hard disks for storing data and other information used by such computer systems. A micro-Winchester disk drive is disclosed in U.S. Pat. No. 4,568,988 to McGinlay et al., issued Feb. 4, 1986, and entitled "Microhard-Disk Drive System." This patent describes a disk drive system that utilizes a 3.5 inch hard disk capable of storing in excess of 5 megabytes of information. A rotary actuated read/write head is provided for accessing the disk tracks. The use of an arcuate movable read/write head is important in reducing the space that is required for the containment and operation of the arm assembly to which the read/write head is attached. Although not directed to a micro disk drive system, U.S. Pat. No. 3,984,873 to Pejcha, issued Oct. 5, 1976, and entitled "Head Loading and Unloading Assembly for a Magnetic Disk Drive Having a Rotary Actuator" also describes a rotary actuated read/write head. This rotary configuration is characterized by the use of spring members and a channel member for use in loading and unloading the read/write head relative to the disk surface. Another rotary actuated assembly is described in U.S. Pat. No. 3,772,666 to Scholz et al., issued Nov. 13, 1973, and entitled "Interlaced Magnetic Heads." This patent discloses a pair of interconnected suspension arms with each of the suspension arms having a number of recording heads attached near the free end of each arm. The interconnecting cross member has a semi-hemispherical cam-riding button located at about the mid portion thereof. During operation, the cam-riding button rests in a depression and when in the non-operative state, the button is caused to move away from the depression using an inclined cam surface. In U.S. Pat. No. 4,535,374, to Anderson et al., issued Aug. 13, 1985, and entitled "Whitney-Type Head Loading/Unloading Apparatus," a triangular-shaped suspension arm is utilized having a generally triangular-shaped ramp located on the under side of the suspension arm. This arm assembly is linearly, not rotary, actuated. The ramp member on the suspension arm engages a cam for providing loading/unloading of the read/write head.
In addition to reducing size and weight in connection with laptop computers, it is also important to make available electric power saving features since laptop computers are typically battery-powered and it is desirable to reduce battery drain. In one portable computer system, it is known to reduce power usage by powering down certain of the disk drive electronics upon the occurrence of a single, predetermined event or condition. The aforesaid U.S. Pat. No. 4,568,988 discloses means for reducing current drawn by a stepper motor when the disk drive has been deselected for two seconds. This reduced power consumption is important, not in saving battery life, but for the purpose of reducing the amount of heat needed to be dissipated and thereby reducing the need for air-extraction fans.
A further important aspect associated with disk drive performance concerns the speed at which track seeks are performed, i.e., the amount of time taken to position the read/write head relative to a target position on the disk. In embedded servo systems, the seek time is a function of the ability of the system to access or sample servo information located at predetermined positions on the disk. Provided that there is sufficient time for the servo information to be processed, it is generally desirable to obtain servo information as often as possible without unduly sacrificing disk storage space. The servo information is used to determine the velocity of the arm assembly including the read/write head attached thereto. Using the velocity magnitude, the movement of the arm assembly can be controlled so that the read/write head is accurately positioned relative to the target position on the disk. In conjunction with conducting a high or rapid performance seek, it would be desirable to use the back electromotive force (emf) of the actuator since the back emf is a continuous signal and therefore provides continuous servo information, in contrast to a sampled data servo system commonly found in embedded servo systems. The actuator is utilized in driving or moving the read/write head and the magnitude of the velocity of the arm assembly is a function of the back emf. However, in prior art systems it has not been practical to extract or accurately identify the back emf generated signal in the presence of the significantly greater-in-amplitude servo correction signal being applied to the actuator.
Another factor influencing the accuracy of servo operation, when a rotary actuator is used, relates to the use of a flexible circuit that interconnects the read/write head(s), servo lines, an electrical ground line and the actuator coil with circuit leads for providing communication with processing or servo-related electronics. Prior art flexible circuits exert a torque on the rotary-actuated arm assembly influencing its movement relative to the disk surface or its position relative to the disk track centerline. In order to properly perform track seeking or track following, the effect of such a torque on the arm assembly must be taken into account and compensated for to eliminate track seeking and following errors. Such compensation is generally handled by compensating circuitry or servo software and the need to perform the compensating steps can add to the seek time, as well as increase the cost of the servo mechanism and decrease the accuracy and reliability of the servo control.
To provide a disk drive apparatus for use with a computer system therefore, a number of different factors affecting the design must be addressed. With regard to the present invention, which employs one or more approximately 2.5 inch (within a size range of about .+-.10%) hard disks, various unique features have been devised in order to implement the about 2.5 inch hard disk concept. These features have resulted in a high performance about 2.5 inch disk drive apparatus, which is characterized by its ruggedness, compact size, reduced weight, rapid and accurate track seeking and power saving modes.